1. Field of the Invention
The invention relates to a method for monitoring and controlling the operation of a dual platen press. The invention is particularly useful where dual platen presses are used in the manufacture of nuclear fuel pellets since small variations in the operation of the press during the manufacture of nuclear fuel pellets can cause undesirable variations in fuel pellet densities and have a deleterious effect on fuel pellet integrity.
2. Background of the Invention
Devices for providing a visual indication or an electrical signal representative of the displacement of a single press platen are common in the prior art. However, these prior art platen displacement indicating devices are found to be of limited usefulness when used with a dual platen press. This is because information regarding the relative displacement and relative velocity of the press platens is required for adequately monitoring and controlling the operation of a dual platen press.
Devices for providing a visual indication of the relative displacement of the platens of a dual platen press may be seen in the prior art. However, these prior art devices generally provide no more than a pair of visual indicators moving simultaneously on a vertical scale. The usefulness of this type of device is limited because information regarding the relative displacement of the platens may be obtained by the observer only by comparing the relative displacements of the two indicators. Also, this type of device provides no indication of the relative velocity of the press platens. Thus, there is a general need in the dual platen press art for a device that accurately records each of the platen displacements of a dual platen press and provides an indication of the relative displacement and relative velocity of the press platens.
In the manufacture of nuclear fuel, normally fuel in the form of UO.sub.2 powder is pressed into pellets which are then sintered and assembled within a tubular cladding to form a complete nuclear fuel element. It is imperative that the fuel pellets be of a known and uniform density for reasons related to the nuclear design of the reactor as well to protect fuel pellet integrity. Variations in the density of the pellet before sintering can result in fuel pellets that crack after sintering or after extended use in a nuclear reactor. Thus, the need for a device that accurately indicates the relative displacement and relative velocity of the platens of a dual platen press is critical where such a press is used in the manufacture of nuclear fuel pellets. Such a device would be used to continuously, or periodically monitor the operation of the press to ensure a maximum yield of acceptable fuel pellets.
Hydraulically actuated dual platen compacting presses are normally used in the manufacture of nuclear fuel pellets since they offer the capability of widely varying a large number of pressing parameters and various UO.sub.2 fuel powders have different pressing requirements. It is common for hydraulically actuated dual platen compacting presses to provide the ability to vary compaction speed, ejection speed, the relative movement of upper and lower platens, compaction pressure and ejection hold-down force. However, experience has shown that it is extremely difficult to determine the proper pressing parameters for a given UO.sub.2 powder and then accurately adjust the compacting press to meet those requirements. Even knowing the correct pressing parameters for a given UO.sub.2 powder it is often extremely difficult to duplicate those parameters when setting up the compacting press. An art dependent upon the skill of the operator rather than a scientifically repeatable procedure has developed associated with determining and/or duplicating the proper press set-up for producing a maximum yield of acceptable fuel pellets from a given type of UO.sub.2 powder. And thus, a need has developed for a device that accurately correlates the various pressing parameters to actual platen displacements, the relative displacement of the platens and relative velocity of the platens. Such a device would be used to aid a press operator both in analyzing press operations for determining a good press set-up and duplicating a press set-up for a given type of UO.sub.2 powder.
In dual or single platen presses, in general, the various portions of the press cycle are initiated and terminated by the displacements of the press platens which actuate various microswitches. The present invention provides a method for generating signals that are used to terminate and intiate various portions of the press cycle without the use of microswitches.
Accordingly, it is a principal object of the present invention to provide a method for controlling the operation of a dual platen press.
Another object of the present invention is to provide a method utilizing both visual and recorded outputs for indicating the relative displacement and relative velocity of the platens of a dual platen press.
Another object of the present invention is to provide a method for accurately recording the platen displacements of a dual platen press and deriving the relative displacement and relative velocity of the platens therefrom for the purpose of monitoring and analyzing the operation of the press.
Another object of the present invention is to provide a method for the manufacture of nuclear fuel pellets which correlates the various pressing parameters of a dual platen press to the actual displacements, the relative displacement and the relative velocity of the press platens for the purpose of more rapidly and accurately determining, or duplicating, the correct pressing parameters for a given type of UO.sub.2 powder.